This invention relates to processing of webs in general and more particularly to a grooved drum, preferably for dehydrating paper, cardboard and similar webs.
Grooved drums with a working drum surface of metal, particularly corrosion resistant steel, consisting of a cylindrical inner drum, on which at least one ribbon is helically wound, turn by turn, which forms, with a radially outer boundary, the working drum surface and forms circumferential grooves axially between these boundaries have been known for a long time, for instance, from the German Patent No. 273 304. The winding of ribbons on an inner drum has also been previously used for making elastic drums with a covering of plastic (German Patent No. 1 038 518). The ribbons have, on the sides facing each other in axial direction, mutually engaging profiles and may be cemented to the inner drum. The application of profiles which engage with each other in succeeding turns is also known, for metal ribbons, specifically through the German Offenlegungsschrift No. 25 45 145. In this embodiment, the ribbon consists of profiled material about 10 to 12 mm high and 2 to 3 mm thick, into the lateral surface of which a longitudinal slot is rolled, which is pressed through on the opposite side as a longitudinal rib; the longitudinal ribs are placed in the longitudinal slots of the adjacent turn. During the winding, the ribbon is under considerable pretension and is pressed on in the axial direction by a roller. The forces resulting from the pretension and the axial pressing force are so large that a plastic deformation of the outer zone of the ribbon ensues, so that the latter assumes a curvature corresponding to the curvature of the circumference of the inner drum.
The profiles of the metal ribbons in the known designs of wound grooved drums are lengthwise. They can therefore hold the succeeding turns against each other in the radial direction, but do not counteract shifting of the turns in the circumferential direction.
If now the ribbon breaks, be it in operation or during the winding, it slips, since the elastic tension force caused by the pretension during the winding is released and the turns are not blocked in the circumferential direction. The drum therefore snaps open, whereby it becomes loose and the drum is made unusable.